Methane in the East China Sea water   总被引：1，自引：0，他引：1  

Nobuo Tsurushima  Shuichi Watanabe  Shizuo Tsunogai 《Journal of Oceanography》1996,52(2):221-233

Methane in the East China Sea water was determined four times at a fixed vertical section along PN line consisting of 11–14 stations, in February 1993, October 1993, June 1994 and August 1994. The mean concentration of methane in the surface water was not significantly higher than that in the open ocean. The methane concentration below the pycnocline increased during the stratified period in summer to autumn and reached to 15 nmoles/l at most in October. The concentration of methane was fairly well correlated with AOU in the layer below the pycnocline in the stratified season. This means that methane in the bottom water has only a single source, which is expected to be anoxic sediments near the coast, and that the oxidation rate of methane in the water is extremely slow in the oxic water. The high methane observed in October completely disappeared in February, indicating that the methane was escaped to the atmosphere or transported to the pelagic ocean by the Kuroshio current. The East China Sea, therefore, is not a large direct and stationary source for the atmospheric methane, but may have some role as a source by supplying it sporadically to the atmosphere in early winter or indirectly from the surface of the pelagic ocean.  相似文献   

Biogeochemical Variation in Dimethylsulfide, Phytoplankton Pigments and Heterotrophic Bacterial Production in the Subarctic North Pacific during Summer     

Kazushi Aranami  Shuichi Watanabe  Shizuo Tsunogai  Masato Hayashi  Ken Furuya  Toshi Nagata 《Journal of Oceanography》2001,57(3):315-322

Dimethylsulfide (DMS), chlorophyll a (Chl-a), accessory pigments (fucoxanthin, peridinin and 19-hexanoyloxyfucoxanthin), and bacterial production (BP) were measured in the surface layer (0–100 m) of the subarctic North Pacific, including the Bering Sea, during summer (14 July–5 September, 1997). In surface sewater, the concentrations of DMS and Chl-a varied widely from 1.3 to 13.2 nM (5.1 ± 3.0 nM, mean ± S.D., n = 48) and from 0.1 to 2.4 µg L^–1 (0.6 ± 0.6 µg L^–1, n = 24), respectively. In the subarctic North Pacific, DMS to Chl-a ratios (DMS/Chl-a) were higher on the eastern side than the western side (p < 0.0001). Below the euphotic zone, DMS/Chl-a ratios were law and the correlation between DMS and Chl-a was relatively strong (r ² = 0.700, n = 27, p < 0.0001). In the euphotic zone, DMS/Chl-a ratios were higher and the correlation between DMS and Chl-a was weak (r ² = 0.128, n = 50, p = 0.01). The wide variation in DMS/Chl-a ratios would be at least partially explained by the geographic variation in the taxonomic composition of phytoplankton, because of the negative correlation between DMS/Chl-a and fucoxanthin-to-Chl-a ratios (Fuc/Chl-a) (r ² = 0.476, n = 26, p = 0.0001). Furthermore, there was a positive correlation between DMS and BP (r ² = 0.380, n = 19, p = 0.005). This suggests that BP did not represent DMS and dimethylsulfoniopropionate (DMSP) removal by bacterial consumption but rather DMSP degradation to DMS by bacterial enzyme.  相似文献   

MOS-1/1b MESSR Observations of the Antarctic Sea Ice: Ice Bands and Ice Streamers     

Kunimitsu Ishida  Kay I. Ohshima  Takashi Yamanouchi  Hiroshi Kanzawa 《Journal of Oceanography》1999,55(3):417-426

Meso- or submeso-scale features of the Antarctic sea ice are investigated using the MOS-1/1b MESSR Images (spatial resolution of approximately 50 m) received at Syowa Station. Particular attention is paid to the ice bands and ice streamers in coastal polynyas. In the Antarctic Ocean, ice bands can be often seen not only at the ice edge but also in the ice interior zone throughout the year and they extend for hundreds of kilometers in the latitudinal direction. It is found that the width and spacing of ice bands tend to decrease from winter to summer. The width of ice band is about 2–6 km in August and September, and 0.1–0.7 km in December. The spacing of ice bands is about 3–10 km in August and September, and 0.1–2 km in December. In coastal polynyas, ice streamers, which are composed of new ice, are sometimes observed. In general, the row of the streamers is spaced at 0.5–2 km with a width of 0.1–1.0 km.  相似文献   

The Current System in the Yellow and East China Seas   总被引：18，自引：1，他引：18  

Hiroshi Ichikawa  Robert C. Beardsley 《Journal of Oceanography》2002,58(1):77-92

During the 1990s, our knowledge and understanding of the current system in the Yellow and East China Seas have grown significantly due primarily to new technologies for measuring surface currents and making high-resolution three-dimensional numerical model calculations. One of the most important new findings in this decade is direct evidence of the northward current west of Kyushu provided by satellite-tracked surface drifters. In the East China Sea shelf region, these recent studies indicate that in winter the Tsushima Warm Current has a single source, the Kuroshio Branch Current in the west of Kyushu, which transports a mixture of Kuroshio Water and Changjiang River Diluted Water northward. In summer the surface Tsushima Warm Current has multiple sources, i.e., the Taiwan Warm Current, the Kuroshio Branch Current to the north of Taiwan, and the Kuroshio Branch Current west of Kyushu. The summer surface circulation pattern in the East China Sea shelf region changes year-to-year corresponding to interannual variations in Changjiang River discharge. Questions concerning the Yellow Sea Warm Current, the Chinese Coastal Current in the Yellow Sea, the current field southwest of Kyushu, and the deep circulation in the Okinawa Trough remain to be addressed in the next decade. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Long-term monitoring of bottom environments of the continental slope off Otsuchi Bay,northeastern Japan     

Kazumasa Oguri  Yasuo Furushima  Takashi Toyofuku  Takafumi Kasaya  Masahide Wakita  Shuichi Watanabe  Katsunori Fujikura  Hiroshi Kitazato 《Journal of Oceanography》2016,72(1):151-166

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A near-inertial current event in the homogeneous deep layer of the northern Sea of Japan during winter     

Michio Watanabe  Toshiyuki Hibiya 《Journal of Oceanography》2018,74(2):209-218

Under strong surface wind forcing during winter, direct current observations in the northern Sea of Japan show the existence of strong near-inertial currents in the deep water that is characterized by the extremely homogeneous vertical structures of temperature and salinity. However, the mechanism generating internal waves in the deep water of the northern Sea of Japan has not been well understood. In this study, to clarify the dynamical link between the surface wind forcing and near-inertial currents in the deep water of the northern Sea of Japan, we drive a general circulation model taking into account realistic wind stress, ocean bottom and land topography. In the northern Sea of Japan, the numerical results show that vertically coherent horizontal currents with a speed of ~ 0.05 m s^?1 are excited throughout the homogeneous deep water. A two-layer model successfully reproduces the pattern of the horizontal current velocities shown by the general circulation model, indicating that internal waves emanate westward from the northwestern coast of Japan through coastal adjustment to the strong wind forcing event and, while propagating into the ocean interior, they excite evanescent near-inertial response throughout the lower layer below the interface.  相似文献   

Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits   总被引：2，自引：2，他引：0  

Akihiko Morimoto  Tetsutaro Takikawa  Goh Onitsuka  Atsushi Watanabe  Masatoshi Moku  Tetsuo Yanagi 《Journal of Oceanography》2009,65(1):61-71

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.  相似文献   

SAR-imaged spiral eddies in Mutsu Bay and their dynamic and kinematic models     

Satoshi Yamaguchi  Hiroshi Kawamura 《Journal of Oceanography》2009,65(4):525-539

A pattern of slick streaks winding into a spiral, known as a spiral eddy, was identified in 5 images taken by the ERS-1/2 synthetic aperture radar (SAR) in Mutsu Bay (Japan); dynamic and kinematic models of these spiral eddies have been proposed. Common characteristics of the five spiral eddies are: 1) an eddy diameter of about 15 km; 2) their location in the western part of the bay; and 3) their cyclonic direction of rotation. Moreover, the wind conditions over the bay were common: prior to acquiring the images, a strong easterly wind continued blowing for more than one day. The wind field on the bay is known to be orographically steered and has strong windstress vorticity, which generates cyclonic circulation. The diameter and location of the circulation simulated with a numerical ocean model corresponded well to those of the identified spiral eddies. Based on these facts, we propose a dynamic model for the movement of a slick streak, and a kinematic model for the formation of a spiral eddy. We have assumed calm air, a microlayer and seawater with a cyclonic circulation in the dynamic model. The balance of forces is established in the microlayer among the frictional force from the seawater, the frictional force from the calm air, the gravitational force, and the Coriolis force. As a result, the velocity vector of the microlayer deflects slightly towards the center of the cyclonic circulation. We have assumed a point source of the microlayer in the kinematic model. The shapes of a slick streak simulated with the models agree well with the identified patterns in the SAR images.  相似文献   

Detecting red tides in the eastern Seto inland sea with satellite ocean color imagery     

Wataru Takahashi  Hiroshi Kawamura  Takuo Omura  Ken Furuya 《Journal of Oceanography》2009,65(5):647-656

A multi-spectral classification scheme is proposed to identify water with red tide(s) using satellite ocean color imagery obtained by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The study area was the eastern Seto Inland Sea in Japan, where serious red tides frequently occur. “Background Ocean Colors” (BOCs hereafter), or colors of water around a red tide or those of the water before/after a red tide, are calculated as the monthly climatological average of normalized water-leaving radiances (nLw) with 0.01 degree spatial resolution with SeaWiFS imagery. Criteria for detecting red-tide pixels are established from analyses of characteristics of the nLws (in the 443, 490, 510, and 555 nm bands) anomalies from BOCs and the nLw spectra together with the red-tide records in Osaka Bay. The proposed scheme can efficiently indicate the presence or absence of red tides for independent match-ups with 83% accuracy. Additional validations of specific events indicate that the algorithm performed well in the study area. These results suggest that the scheme is appropriate to detect red tides in the optically complex coastal water of the eastern Seto Inland Sea.  相似文献   

Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region     

Hiroshi Ishida  Yutaka W. Watanabe  Joji Ishizaka  Toshiya Nakano  Naoki Nagai  Yuji Watanabe  Akifumi Shimamoto  Nobuhiro Maeda  Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.  相似文献